Apparatus for oxidizing residual pulp liquor



INVENTGRS ROBERT K, ALLEN &

Aug. 7, 1956 R. K. ALLEN EIAL APPARATUS FOR oxwrzmc RESIDUAL PULP LIQUORFiled July so, 1949 2 Sheets-Sheet 1 BY JAMES H (OZ/175A, JA. fill gRNEYF/GJ 7, 1955 R. K. ALLEN EI'AL 2,758,017

APPARATUS FOR CXIDIZING RESIDUAL PULP LIQUOR Filed July 50, 1949 2Sheets-Sheet 2 INVENTORS 05597 K. AME/Va? BY JAME H.60ULTEE, JA

0% ATTORNEY United States Patent APPARATUS FOR OXIDIZING RESIDUAL PULPLIQUOR Robert K. Allen, Waldwick, N. J., and James H. Coulter, Jr.,Franklin Square, N. Y., assignors to The Babcock & Wilcox Company, NewYork, N. Y., a corporation of New Jersey Application July 30, 1949,Serial No. 107,776

6 Claims. (Cl. 23-283) The present invention relates to the recovery ofchemicals in the residual liquor resulting from the chemical pulping ofcellulosie fibrous materials. More particularly the invention relates toa method of and apparatus for the stabilization of sulphur compounds insulphate residual liquors by the oxidation of the weak liquor atgenerally atmospheric temperatures.

The residual liquor resulting from the digestion of cellulosic materialsin the sulphate process of paper pulp manufacturing contains sulphurcompounds which are unstable when subjected to heat or heat in thepresence of carbon dioxide gases. The principal unstable sulphurcompound in the pulp residual liquor is sodium sulphide (NaaS), althoughsmaller amounts of other unstable compounds, such as mercaptans, arealso present. These sulphur compounds evolve noxious gases, such ashydrogen sulphide, during concentration and incineration of the residualliquor. Such noxious gases not only are a nuisance, but upon theirescape from the process also involve an appreciable economic loss ofsulphur. However, it is known in the art that the unstable sulphurcompounds can be stabilized by oxidation of the liquor in contact withan oxygen containing gas, such as air, at generally atmospherictemperatures and pressures. The oxidation of the liquor converts thesodium sulphide, for example, to a stable compound, sodium thiosulphate(NazSzOa).

In general, two methods of oxidation can be used to stabilize thesulphur compounds in a sulphate residual liquor. One method includesforcing air or other oxygen containing gases through a sheet or bathofthe liquor. This results in an effective mechanical contact betweenthe liquor and the gas, and a high degree of liquor oxidation. However,this method results in the formation of large quantities of foam,necessitating the use of a foam breaker or the provision of settlingtanks for the foam. The second method of liquor oxidation seeks to avoidor minimize the formation of foam, so that the foam handling equipmentwill be but a minor portion of the apparatus required for thestabilization of the sulphur compounds in the residual liquor.

The present invention relates to a method of and apparatus for theoxidation of residual liquor under conditions of a minimum formation offoam. The liquor is.

passed through a tower in a plurality of films in countercurrent surfacecontact with the oxidizing gas, with the liquor filmsformed at the topof the tower in such a manner as to avoid the passage of oxidizing gasesthrough any body of liquor. Any foam formed in the lower portion of thattower is removed, as formed, so as to avoid pluggage of the gas flowpassages through the upper portion of. the tower.

The various features of novelty which characterize this invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and Patented Aug.7, 1956 ice descriptive matter in which the invention has beenillustrated and described.

Of the drawings:

Fig. 1 is an elevation view of an oxidation tower constructed inaccordance with the present invention;

Fig. 2 is an enlarged elevation view, in section, of a part of the upperportion of the apparatus shown in Fig. 1;

Figs. 3 and 4 are section views taken along the lines 3-3 and 44,respectively, of Fig. 2

Figs. 5 and 6 are enlarged views of the support and guide elements,respectively, of the secondary distribution pans shown in Figs. 2 and 3;and

Fig. 7 is a plan view, in section, of a modified construction andarrangement of the tower walls shown in Fig. 1.

In general, as shown in the drawings, the liquor oxidizing apparatus ofthe present invention includes a vertically elongated cyclindrical shell16 defining a liquorgas surface contact tower. The tower is providedwith a gas outlet 11 and liquor inlet pipes 12 and 13 in its upper endportion, and a gas inlet duct 15 intermediate the height of the towerconnected with a source of supply such as a fan 18, and a liquor outletpipe 14 in its lower end portion. Between the vertically spaced liquorinlet pipes and the gas inlet duct the tower is provided with aplurality of vertically extending horizontally spaced walls 16 arrangedto present an extensive area of surface contact between the liquor andthe oxidizing gas. Exteriorly of the tower shell 10, a liquor pump 17 isarranged to withdraw oxidized liquor through the pipe 14 and todischarge a selected portion of the liquor through the pipe 12 torecirculate through, and thereby to control the degree of liquoroxidation attained within the tower.

As shown in Figs. 1 and 2, the shell lit of the tower is provided with afrusto-conical top 2t) having a centrally positioned opening thereindefining the gas outlet 11. The recirculated liquor supply pipe 12 andthe make-up liquor supply pipe 13 project through the conical sides ofthe top 20 to discharge into a primary liquor distribution pan 21 of agenerally circular plan section. From the pan 21 the liquor isdischarged through connecting tubes 22 to a plurality of horizontallydisposed secondary liquor distribution pans 23. Each of the pans 23 isprovided with an individual tube 22 which is arranged with its lower endspaced above the bottom of the pan and generally centered with respectto the pan walls. The upper end of each tube 22 is fitted with avertically adjustable notch or orifice, so that the intake height ofeach tube equal to each of the other tubes, and each or" the tubes 22receives a substantially equal share of the liquor discharged to thepans 23. As shown in Fig. 2, the adjustable orifice on the upper end ofeach of the tubes 22 is formed from a pipe coupling 28 which is notchedand threaded to the upper end of a tube.

The pans 23 are arranged in spaced horizontal relationship as shown inFigs. 2 and 3, and are each provided with a plurality of rows of spacedoutlet ports 24 in the bottom thereof. The spacing between the rows ofports 24 corresponds with the spacing between the extended surface walls16 of the tower, so that when the pans are properly positioned the portsare in vertical alignment with the walls with the discharging liquorforming a film on each of the vertical wall surfaces. The

proper positioning of the pans is obtained and maintained by the use ofguide clips 2 fastened to the under side of the pans, and each arrangedto engage the upper end of one of the subjacent tower walls. For bestresults in the oxidizing tower, the liquor should be distributed to allof the subjacent wall surfaces so as to utilize the maximum availablearea of liquor film for gas contact therewith. Best distribution ofliquor is obtained by leveling each of the pans 23 with generally equalquantitles of liquor passing through each of the ports 24. Each pan issupported upon the subjacent walls 16 of the tower, With each of the pansupports formed by an adjustable screw jack 38. The detailed arrangementof the guide clips 29 and the screw jacks 33 is shown in Figs. 6 andrespectively, while their assembled relationship to the pans 23 is shownin plan view in Fig. 3.

Each of the secondary distributing pans 23 is provid'ed with two or moregas passage tubes 25 fastened to the bottom of the pan and arranged withtheir lower ends opening into the space between adjacent walls 16. Thetubes 25 extend upwardly above the surface of the liquor pool maintainedin the pans 23.

As shown in Fig. l, the walls 16 of the tower extend substantiallyvertically from an upper position, indicated at 42, which is closelyspaced below the distributing pan 23, to a lower position intermediatethe height of the oxidizing tower. The walls are supported at theirlower ends by a support grid 44 attached to the shell 10. As shown inFigs. 2 and 4, the walls 16 are constructed and arranged to extendtransversely across the interior of the shell in closely spaced parallelrelationship. The horizontal spacing between adjacent walls ismaintained by a plurality of spacing strips 43 which are substantiallyuniform in cross-sectional dimensions and extend vertically for the fullheight of the walls 16. Each surface of the walls is constructed to forma continuous, substantially planar surface throughout its verticalheight, so that the liquor film flowing downwardly along the wallsurface will be uninterrupted. In horizontal section, the walls are thusarranged to define a multitude of rectangular passageways for the upwardflow of the oxidizing gas.

The walls 16 can be constructed of any suitable material that issubstantially inert with respect to the liquor. Wood has been usedsuccessfully as a material, with the walls 16 fabricated from one inchlumber. When the tower is in use with new wood, the weak liquor willdissolve and remove the hemicellulose in the wood. This attack on thepacking results in a loss of approximately 20 percent of the weight ofthe wood, without serious loss of structural strength, and is ended inthe first hours of initial liquor and wood contact. After the removal ofthe hemicellulose the wood is substantially inert with respect to theliquor under the temperature and pressure conditions prevailing withinthe tower.

The spacing of the ports 24 in the bottom of the distributing pan 23 isselected to match the dimensions of the walls 16 and the spacing strips43, so that the liquor streams will impact the upper surfaces of thewalls. The assembled relationship of the ports 24 with the upper ends ofthe walls 16 is shown particularly in Fig. 2. The spacing between theadjacent pans 23 and the gas passage tubes 25 will direct the oxidizinggas flow with a minimum interference in the formation of the liquorfilms on the walls 16. This arrangement will tend to cause the liquorfilms on the wall surfaces to be formed with a minimum of liquorfoaming, as may be created by a flow of gas through the liquor streams.

The lower portion of the tower is provided with vertically spacedinverted frusto-conical members 26 and 27 extending across thecross-sectional area of the shell 10. The uppermost member 26 is spacedbelow the grid 44 and the gas inlet duct 15, and is arranged to receivethe oxidized liquor discharging from the lower ends of the walls 16. Theliquor collected in the member 26 passes through a centrally positionedoutlet into a discharge pipe 30. Since it is advantageous to-avoid afree fall of liquor, so as to reduce foam formation, the pipe 30 isarranged to discharge liquor from'the lower end thereof in a directiongenerally tangential to and adjacent the inner surface of the shell 10.The lower member 27 isprovided with a centrally located opening 31 whichis connected with the pipe 14 by means of a vertically 4 arranged stubpipe 32 and a connecting T fitting 33. The fitting 33 is provided with adrain valve 34 so that the tower can be washed during periods of towerrepair or cleaning.

The oxidized liquor flow rate through the pump 17 is regulated by thevalves 35 and 36 in the pump inlet and discharge lines, respectively.The liquor leaving the pump is ordinarily divided into two streams, onestream passing through a valve 37 into the pipe 12 for recirculationthrough the oxidation tower, while the other stream passes through avalve 40 and a pipe 41. The pipe 41 may be connected to an oxidizedliquor storage tank, or directly connected with a liquor concentratingdevice, such as a multiple effect evaporator. The liquor fiow througheither of the pipes 12 and 41, or through both in any selectedproportion, can be easily regulated by adjustment of the valves 37 and40.

A pool of oxidized liquor is maintained within the bottom of the towerso as to provide a source of liquor, free of foam, for the pump 17inlet. Any foam accumulated in the section of the tower defined betweenthe'members 26 and 27 will float on the top 47 of the liquor pool. Whenthe height of the foam reaches the level of a foam discharge pipe 50,the foam is removed by a foam pump 51 for delivery through a pipe 52 toa settling tank (not shown). While a source of foam-free liquor isdesirable for the pump 17, the level of the pool of liquor in the lowerportion of the tower can also be used as a means for regulating theamount of unoxidized or make-up liquor supplied to the tower through thepipe 13. With the operational adjustment of the amount of oxidizedliquor recirculated through the pipe 12, the actual amount of oxidizedliquor removed from the system through the pipe 41 and thus the amountof make-up liquor required to maintain a generally uniform flow ofliquor through the tower packing, may change. Any necessary changes inflow of liquor through the pipe 13 are readily accomplished by a float53 operatively connected to a flow control valve 54 positioned in thepipe 13, through a linkage 55. The float 53 is selected with a weightand dimension sufiicient to be effected only by the level 47 of theliquor pool, and not by any variation in the amount of foam present.

A modified arrangement of the tower packing is shown in Fig. 7. As inthe arrangement of Figs. 2 and 4, all of the vertical surfaces of thepacking are continuous and planar from top to bottom. In the arrangementof Fig. 7, the horizontal section of the spaces between the walls istriangular. The spacing between adjacent walls 16' is substantiallyequal to the spacing between successive spacing strips 43', with thesubstantially square spaces therebetween divided by a diagonal member45. The

- ports 24' through which the liquor is delivered to the top of thepacking are spaced and arranged to discharge the liquor so as to form adownwardly moving film on each of the vertical surfaces of the packing.

The oxidizing function of the apparatus is initiated by starting the fan18 to circulate the oxidizing gas through the packing of the tower.After a short period of gas flow, liquor is supplied to the top of thetower through the pipe 13. The liquor pools maintained in the reservoir21 and the distributing pan 23 are not subjected to a flow of gastherethrough, and thus any substantial foaming of the liquor is notencountered at these positions. Although the liquor ports 24 or 24 aresubjected to a slight gas pressure, such pressure is insufiicient toovercome the head of liquor maintained in the pan 23, so that gas flowupwardly through the liquor pool therein is avoided. The gas leaving theupper end of the walls of the packing will flow through the pipes 25,between the spaced pans, and between the periphery of the pans and theinterior of the shell. 10. While the streams of liquor dischargingthrough the ports 24 fall through a short distance to the subjacent topsof the walls 16, and in so falling are exposed to a limited cross flowof gas, the foam formed is slight and will be washed downwardly throughthe tower by the liquor flow and will not interfere with either gas orliquor flow in the upper portion of the shell 10. p

The surface contact between the liquor films on the walls 16 or 16 andthe ascending gas effectively oxidizes the liquor to stabilize theunstabilized sulphur compounds therein, while minimizing foam formation.As the liquor falls through the gas inlet space between the support grid44 and the member 26 foam is formed on contact with the latter. However,the foam will be washed down through the pipe 30 by the downflowingliquor and will not accumulate sufficiently to block or adverselyrestrict the gas flow passages between the walls of the tower packing.

As the liquor level 47 rises to the desired position, the inflow ofmake-up liquor is progressively reduced, as automatically regulated bythe valve 54 and the float 53. With a pool of liquor in the member 27the pump 17 is started. During the initial operating period of the pump17, the oxidized liquor discharged therefrom is ordinarily recirculatedto the reservoir 21 by adjustment of the valves 37 and 40. As thedesired degree of liquor oxidation is attained the valves 37 and 40 arereadjusted to discharge oxidized liquor through the pipe 41. Whenstabilized operating conditions have been established for the desiredliquor oxidation, the apparatus will maintain such conditionsautomatically by reason of the make-up liquor flow control.

The amount of sodium sulphide contained in residual Kraft liquor willvary from plant to plant, depending upon the raw materials in use.However, for purposes of illustration a sodium sulphide content ofapproximately .006 pound per pound of liquor may be considered typicalof the residual liquor obtained from the pulping of southern pine, forexample. The height of the tower described, i. e. the vertical extent ofthe walls 16 required to oxidize sodium sulphide to sodium thiosulphatedepends upon the sulphide content of the entering liquor and the degreeof oxidation desired. For each .001 pound of the sulphide per pound ofliquor supplied, the tower must be from approximately 6 to 13 feet high,where the smaller dimeni.-:

lation increases the amount of liquor passing through the i tower andnecessitates larger areas of liquor-gas contact.

The tower described has been successfully operated at liquor flow ratesof from 50 to 400 pounds per hour of liquor per foot of wetted wallperimeter. Below the lower value the volume of liquor seems to beinsuflicient to cover the available surfaces of the walls 16 or 16.Above 400 pounds per hour the liquor film seems to become too thick forbest contact with an oxidizing gas, such as air. In this range of liquorflow rates the oxidizing air, substantially at atmospheric temperatureand pressure, is passed through the tower at a rate corresponding tofrom approximately .015 to .05 pound of air per pound of liquor.Apparently, the air flow velocity through the tower should be low, butvelocity does not seem to be critical, as long as the velocity of theair flow does not interfere with the downwardly moving liquor films. Thegeneral proportions of the air flow passageways between the filmsupporting walls illustrated in the drawings, have proven satisfactoryfor this purpose.

It will be understood the tower of the present invention is constructedand arranged for the oxidation of unstabllized sodium compounds in aresidual pulp liquor. For any particular tower, constructed according tothe present invention, a reasonably consistent weight of sodium sul- 6phide will be oxidized to sodium thiosulphate within the flow limitsdescribed for air and liquor. When the weight of sodium sulphide in themane-up or untreated liquor is sufficiently low, or when substantiallycomplete oxidation is unnecessary, the tower can be operated without therecirculation of partially oxidized liquor. Several towers may also beconnected for series flowof liquor, without recirculation, when a highweight ratio of sodium sulphide is present in the untreated residualliquor. Under desired operating conditions of partial liquor oxidation,the tower may be operated without the use of a fan, and with air flowingthrough the tower by reason of natural draft. Due to the very slightdifference in entering air and liquor temperatures very littleconcentration of liquor occurs during its treatment in the oxidizingtower of the present invention. Ordinarily the contact between air andliquor will cause some evaporation of moisture from the liquor. but theamount is insignificant.

While in accordance with the provisions ofthe statutes we haveillustrated and described herein the best form and mode of operation ofthe invention now known to us, those skilled in the art will understandthat changes may be made in the form of the apparatus disclosed withoutdeparting from the spirit of the invention covered by the claims,andthat certain features of the invention.

may sometimes be used to advantage without a corresponding use of otherfeatures.

We claim:

1. Apparatus for the oxidation of a pump residual liquor substantiallywithout evaporation comprising a tower, a plurality of verticallyextending continuous planar walls in the intermediate and upper portionon said tower, a liquor distributor having a perforate bottom positionedadjacent the upper end of said tower walls, said distributor arranged tomaintain a pool of liquor therein and to deliver a plurality of streamsof liquor to and in substantial vertical alignment with said walls,means for passing a flow of air between said walls in direct surfacecontact relationship with films of liquor thereon, and a plurality ofair discharge pipes extending through said liquor distributor and thepool of liquor therein, whereby air leaves said tower without passingthrough said liquor pool.

2. Apparatus for the oxidation of a pulp residual liquor substantiallywithout evaporation comprising a tower, wood walls within said towerarranged to form a plurality of vertically extending continuous planarsurfaces arranged to form a plurality of gas flow passagewaystherebetween of substantially uniform horizontal configuration, a liquordistributor pan adjacent the upper end of said walls arranged to enclosea pool of liquor therein and having a plurality of perforations thereinsubstantially in vertical alignment with the top of said walls todeliver streams of liquor to said walls, means for passing a flow of airthrough said passageways in direct contact surface relationship with theliquor on said walls, and a plurality of air discharge pipes extendingthrough said liquor pan whereby air leaves said tower without passingthrough said liquor pool.

3. Apparatus for the oxidation of a pulp residual liquor comprising aclosed tower having a top gas outlet and a bottom liquor outlet therein,a plurality of horizontally spaced substantally vertical walls extendingfrom a position adjacent the top of said tower to a position spacedabove the bottom of said tower, a liquor distributing pan positionedclosely adjacent the upper end of said walls and having a plurality ofperforations therein spaced to discharge streams of liquor to the top ofeach of said walls, means for maintaining a pool of liquor in said pan,a plurality of tubes extending upwardly through said pan with the lowerends thereof opening to the spaces between adjacent walls, a fanarranged to deliver oxidiz ing gas to said tower for upward flow betweensaid walls and through said tubes to said gas outlet, an invertedfrusto-conical liquor collecting member extending across said tower at aposition intermediate the lower end of said vertical walls'andsaid'tower bottom, a discharge tube connected with a centrallypositioned opening in said member and extending to a lower positionspaced above said tower bottom adapted to discharge liquor generallytangentially along the wall of said tower, and a pump arranged towithdraw liquor from the bottom of said tower.

4. Apparatus for the oxidation of a pulp residual liquor comprising aclosed tower having a top gas outlet and a bottom liquor outlet therein,a plurality of horizontally spaced substantially vertical wallsextending from a position adjacent the top of said tower to a positionspaced above the bottom of said tower, a liquor distributing panpositioned closely adjacent the upper end of said walls and having aplurality of perforations therein spaced to discharge streams of liquorto the top of each of said walls, means for maintaining a pool of liquorin said pan, a plurality of tubes extending upwardly through said panwith the lower ends thereof opening to the spaces between adjacentwalls, a fan arranged to deliver oxidizing gas to said tower for upwardfiow between said walls and through said tubes to said gas outlet, aninverted frusto-conical liquor collecting member extending across saidtower at a position intermediate the lower end of said vertical wallsand said tower bottom, a discharge tube connected with a centrallypositioned opening in said member and extending to a lower positionspaced above said tower bottom adapted to discharge liquor generallytangentially along the wall of said tower, a pump arranged to withdrawliquor from the bottom of said tower, and a float adapted to control theflow of liquor to said pan in response to the level of liquid in thebottom of said tower.

5. Apparatus for the oxidation of a pulp residual liquor comprising aclosed tower having a top gas outlet and a bottom liquor outlet therein,a plurality of horizontally spaced substantially vertical wallsextending from a position adjacent the top of said tower to a positionspaced above the bottom of said tower, a liquor distributing panpositioned closely adjacent the upper end of said walls and having aplurality of perforations therein spaced to discharge streams of liquorto the top of each of said walls, means for maintaining a pool of liquorin said pan, a plurality of tubes extending upwardly through said panwith the lower ends thereof opening to the spaces between adjacentwalls, a conduit opening into said tower at a position beneath the lowerend of said vertical walls and arranged to deliver air to said tower forupward flow between said walls and through said tubes to said gasoutlet, an inverted frustoconical liquor collecting member extendingacross said tower at a position intermediate the lower end of saidvertical walls and said tower bottom, a discharge tube connected with acentrally positioned opening in said member and extending to a lowerposition spaced above said tower bottom adapted to discharge liquorgenerally tangentially along the wall of said tower, a pump arranged towithdraw liquor from the bottom of said tower, and a float adapted tocontrol the flow of liquor to said pan in response to the level ofliquid in the bottom of said tower.

6. Apparatus for the oxidation of pulp residual liquor comprising aclosed tower having a gas outlet in its top and a liquor outlet in itsbottom, a plurality of horizontally spaced substantially vertical wallsextending from a position adjacent the top of said tower to a positionspaced above the bottom of said tower, a liquor distributing panpositioned closely adjacent the upper end of said walls and having aplurality of perforations therein spaced to discharge streams of liquorto the top of each of said walls, a plurality of gas flow tubesextending upwardly through said pan with the lower ends thereof openinginto the spaces between adjacent walls, an inverted frusto-conicalliquor collecting member extending across said tower at a positionintermediate the lower end of said vertical walls and said tower bottom,a discharge tube connected with a centrally positioned opening in saidmember and extending to a lower position spaced above said tower bottomadapted to discharge liquor tangentially along the wall of said tower, aliquor pump arranged to withdraw liquor from the bottom of said towerand to discharge a selected portion of said liquor into saiddistributing pan, means for delivering make-up liquor to said pan, meansfor controlling the flow of make-up liquor in response to the level ofliquor in the bottom of said tower, and a fan arranged to deliver anoxygen containing gas to said tower for upward flow between said walls.

References Cited in the file of this patent UNITED STATES PATENTS146,728 Ungeur Ian. 20, 1874 341,316 Cochrane May 4, 1886 1,445,603Robeson Feb. 13, 1923 1,654,181 Mann Dec. 27, 1927 1,847,845 Mullen Mar.1, 1932 1,855,353 Jacobson Apr. 26, 1932 2,042,127 Sayles May 26, 19362,139,827 Johnstone et a1. Dec. 13, 1938 2,317,951 Burk Apr. 27, 19432,570,460 Kress Oct. 9, 1951 2,574,193 Savell Nov. 6, 1951 OTHERREFERENCES Haegglund: Paper Trade Journal, Technical Sect., page 50,December 16, 1926. (Copy in Scientific Library.)

Enderlein: Paper, vol. 29, No. 12, November 23, 1921, pages 9 and 10.(Copy in Scientific Library.)

1. APPARATUS FOR THE OXIDATION OF A PUMP RESIDUAL LIQUOR SUBSTANTIALLYWITHOUT EVAPORATION COMPRISING A TOWER, A PLURALITY OF VERTICALLYEXTENDING CONTINUOUS PLANAR WALLS IN THE INTERMEDIATE AND UPPER PORTIONON SAID TOWER, A LIQUOR DISTRIBUTOR HAVING A PERFORATE BOTTOM POSITIONEDADJACENT THE UPPER END OF SAID TOWER WALLS, SAID DISTRIBUTOR ARRANGED TOMAINTAIN A POOL OF LIQUOR THEREIN AND TO DELIVER A PLURALITY OF STREAMSOF LIQUOR TO AND IN SUBSTANTIAL VERTICAL ALIGNMENT WITH SAID WALLS,MEANS FOR PASSING A FLOW OF AIR BETWEEN SAID WALLS IN DIRECT SURFACECONTACT RELATIONSHIP WITH FILMS OF LIQUOR THEREON, AND A PLURALITY OFAIR DISCHARGE PIPES EXTENDING